I think that there could be a variety of approaches here.  The first would be to define "national security."  Obviously, Stalin and other Soviet voices saw the acquisition of "satellite states" as an act of national security. The idea here was that Stalin was afraid of leaving the Western border unprotected, making the Soviet Union susceptible to attack as it was by Germany in World War II.  The consolidation of Soviet power was evident in the takeover of a large number of border states, constructing them as "buffer states."  This could be seen as national security, from the Soviet viewpoint.  Yet, I think that an equally compelling case could be made that this action was more aggressive than "national security."  In terms of examining how the United States was in this light, I think that the Soviet annexation of states was more aggressive than what the United States was pursuing.  Its intervention in different parts of the world could be seen as national security, in much of the same light as the Soviets.  Yet, I think that Soviet outward expansion into neighboring states is more aggressive, on the whole, moving outside of the realm of "national security" and into the realm of nation expanding.